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Abstract:

A defect inspection method includes an illumination light adjustment step
of adjusting light emitted from a light source, an illumination intensity
distribution control step of forming light flux obtained in the
illumination light adjustment step into desired illumination intensity
distribution, a sample scanning step of displacing a sample in a
direction substantially perpendicular to a longitudinal direction of the
illumination intensity distribution, a scattered light detection step of
counting the number of photons of scattered light emitted from plural
small areas in an area irradiated with illumination light to produce
plural scattered light detection signals corresponding to the plural
small areas, a defect judgment step of processing the plural scattered
light detection signals to judge presence of a defect, a defect dimension
judgment step of judging dimensions of the defect in each place in which
the defect is judged to be present and a display step of displaying a
position on sample surface and the dimensions of the defect in each place
in which the defect is judged to be present.

Claims:

1. A defect inspection method comprising: an illumination light
adjustment step of adjusting light emitted from a light source to light
flux having desired light amount, position, beam diameter and
polarization state; an illumination intensity distribution control step
of leading the light flux obtained in the illumination light adjustment
step to a surface of a sample with a desired incident angle and forming
illumination intensity distribution which is long in one direction and
short in a direction perpendicular to the one direction on the surface of
the sample; a sample scanning step of displacing the sample in a
direction substantially perpendicular to a longitudinal direction of the
illumination intensity distribution in an illumination light irradiation
position on the surface of the sample by the illumination intensity
distribution control step; a scattered light detection step of counting
number of photons of scattered light emitted from plural small areas in
an area irradiated with illumination light by the illumination intensity
distribution control step in the sample scanning step to produce plural
scattered light detection signals corresponding to the plural small
areas; a defect judgment step of processing the plural scattered light
detection signals obtained in the scattered light detection step to judge
presence of a defect; a defect dimension judgment step of processing the
scattered light detection signal relevant to each place in which the
defect is judged to be present in the defect judgment step to judge
dimensions of the defect; and a display step of displaying position on
the surface of the sample for each place in which the defect is judged to
be present in the defect judgment step and the dimensions of the defect
obtained in the defect dimension judgment step.

2. A defect inspection method according to claim 1, wherein in the
scattered light detection step, plural scattered light components emitted
in plural mutually different directions of the scattered light emitted
from the sample in the sample scanning step are detected to produce
plural relevant scattered light detection signals, and in the defect
judgment step, at least one signal of the plural scattered light
detection signals obtained in the scattered light detection step is
processed to judge present of the defect.

3. A defect inspection method according to claim 1 or 2, wherein in the
scattered light detection step, the scattered light is led to plural
avalanche photodiode pixels arranged two-dimensionally and operated in a
Geiger mode so that each of the scattered light emitted from the plural
small areas is received by the plural avalanche photodiode pixels to
produce a signal obtained by adding signals of the plural avalanche
photodiode pixels for each relevant small area.

4. A defect inspection method according to claim 3, wherein in the
scattered light detection step, an image of a minute defect extends over
the plural avalanche photodiode pixels in a direction substantially
perpendicular to the longitudinal direction of the illumination intensity
distribution.

5. A defect inspection method according to claim 3, wherein in the
scattered light detection step, an image of a minute defect extends over
the plural avalanche photodiode pixels in a direction substantially
perpendicular to the longitudinal direction of the illumination intensity
distribution.

6. A low light detecting method comprising: a refocusing step of
enlarging an image by low light emitted from an area which is long in one
direction (X direction) and short in a direction (Y direction)
perpendicular to the one direction in the surface of the sample to be
refocused; and a signal outputting step of detecting light intensity
distribution on a surface of an image refocused on a two-dimensional
array sensor having the surface of the image refocused in the refocusing
step as a light receiving surface and outputting a total of detection
signals of pixels arranged in the Y direction of the array sensor.

7. A low light detecting method according to claim 6, wherein an electron
multiplication factor of light detection pixels constituting the array
sensor in the signal outputting step is equal to or larger than 10.sup.4.

9. A low light detector comprising: avalanche photodiodes arranged in
two-dimensional gridlike fashion (X and Y directions) and operating in a
Geiger mode; and wherein a total of detection signals in a column of the
avalanche photodiodes in the X direction is outputted for each row in the
Y direction of the avalanche photodiodes.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a defect inspection method, a low
light detecting method and a low light detector for inspecting a minute
defect existing on the surface of a sample and judging a position, a kind
and dimensions of the defect to be outputted.

BACKGROUND ART

[0002] In a manufacturing line of semiconductor substrates, thin-film
substrates and the like, in order to maintain and improve the yield of
products, inspection of a defect existing on the surface of the
semiconductor substrates, the thin-film substrates and the like is
performed. As prior arts of the defect inspection, JP-A-8-304050 (Patent
Literature 1), JP-A-2008-268140 (Patent Literature 2) and the like are
known.

[0003] The Patent Literature 1 describes that "the same defect is
illuminated plural time in one inspection by an illumination optical
system which makes linear illumination and a detection optical system
which divides an area to be illuminated by a line sensor and detects a
defect and scattered light therefrom is added to thereby improve the
detection sensitivity".

[0004] The Patent Literature 2 describes that "2n APD's corresponding to
laser light bands are arranged linearly" and "proper pairs of the 2n
APD's are combined to calculate differences in output signals of the
combined paired APD's, so that noise due to reflected light is erased and
defect pulse for scattered light is outputted".

CITATION LIST

Patent Literature

[0005] Patent Literature 1: JP-A-8-304050

[0006] Patent Literature 2:
JP-A-2008-268140

SUMMARY OF INVENTION

Technical Problem

[0007] The defect inspection used in the manufacturing process of
semiconductors and the like demands detection of a minute defect,
high-accuracy measurement of dimensions of the detected defect,
inspection of a sample without destruction (for example, without changing
the sample in quality), acquisition of substantially fixed inspection
results in terms of the number, position, dimensions and a kind of a
detected defect, for example, in case where the same sample is inspected,
inspection of a large number of samples within a fixed time and the like.

[0008] In the technique described in the Patent Literatures 1 and 2,
particularly minute defect having the dimension equal to or smaller than
20 nm, for example, cannot be detected since scattered light emitted from
the defect is extremely low and a defect signal is buried in noise caused
by scattered light emitted from the surface of the sample or noise of a
detector or a detection circuit. Alternatively, in order to avoid it,
when illumination power is increased, the temperature of the sample by
illumination light is increased highly, so that thermal damage is caused
to the sample. Alternatively, in order to avoid it, when the scanning
speed of the sample is reduced, the area of the sample or the number of
samples which can be inspected within a fixed time is reduced. As
described above, it is difficult to detect the minute defect at a high
speed.

[0009] As a method of detecting low light, a photon counting method is
known. Generally, the photon counting in which the number of detected
photons for low light is counted is performed to thereby improve the SN
ratio of signal and accordingly the stable signal with high sensitivity
and high accuracy can be obtained. As an example of the photon counting
method, there is known a method of counting the occurrence number of
pulse currents generated in response to incidence of photons on a
photomultiplier or avalanche photodiodes. When plural photons enter or
impinge in a short time and the pulse currents are generated plural
times, it is impossible to count the pulse currents and accordingly an
amount of light cannot be measured with high accuracy and the method
cannot be applied to the defect inspection.

[0010] Further, as a method of another photon counting method, there is
known a method of measuring the total of pulse currents generated in
response to incidence of photons on pixels of a detector having a large
number of avalanche photodiode pixels arranged. This detector is named
Si-PM (Silicon Photomultiplier), PPD (Pixelated Photon Detector) or MPPC
(Multi-Pixel Photon Counter). According to this method, the light amount
can be measured even when plural photons enter in a short time as
different from the photon counting using the above single photomultiplier
or the avalanche photodiodes. However, since the large number of arranged
avalanche photodiodes are operated as a detector having one "pixel", this
method cannot be applied to the high-speed or high-sensitive defect
inspection due to parallel detection of plural pixels.

Solution to Problem

[0011] In order to solve the above problems, the structure described in
the Claims is adopted, for example.

[0012] The present invention includes plural measures for solving the
above problems and an example thereof is described as follows: an
illumination light adjustment step of adjusting light emitted from a
light source to light flux having desired light amount, position, beam
diameter and polarization state, an illumination intensity distribution
control step of leading the light flux obtained in the illumination light
adjustment step to a surface of a sample with a desired incident angle
and forming illumination intensity distribution which is long in one
direction and short in a direction perpendicular to the one direction on
the surface of the sample, a sample scanning step of displacing the
sample in a direction substantially perpendicular to a longitudinal
direction of the illumination intensity distribution in an illumination
light irradiation position on the surface of the sample by the
illumination intensity distribution control step, a scattered light
detection step of counting the number of photons of scattered light
emitted from plural small areas in an area irradiated with illumination
light by the illumination intensity distribution control step in the
sample scanning step to produce plural scattered light detection signals
corresponding to the plural small areas, a defect judgment step of
processing the plural scattered light detection signals obtained in the
scattered light detection step to judge presence of a defect, a defect
dimension judgment step of processing the scattered light detection
signal relevant to each place in which the defect is judged to be present
in the defect judgment step to judge dimensions of the defect and a
display step of displaying position on the surface of the sample for each
place in which the defect is judged to be present in the defect judgment
step and the dimensions of the defect obtained in the defect dimension
judgment step are provided.

Advantageous Effects of Invention

[0013] According to the present invention, there can be provided a defect
inspection method, a low light detecting method and a low light detector
which can scan all surface of a sample in a short time to detect a minute
defect while reducing thermal damage caused to the sample, can calculate
dimensions of the detected defect with high accuracy and can produce
stable inspection result.

[0014] Other problems, structures and effects except the above will be
apparent from the following description of embodiments.

BRIEF DESCRIPTION OF DRAWINGS

[0015]FIG. 1 is a schematic diagram illustrating the whole structure of
an embodiment of a defect inspection device according to the present
invention;

[0016]FIG. 2 is a diagram showing a first example of an illumination
intensity distribution shape realized by an illumination part according
to the present invention;

[0017]FIG. 3 is a diagram showing a second example of an illumination
intensity distribution shape realized by the illumination part according
to the present invention;

[0018]FIG. 4 is a diagram showing a third example of an illumination
intensity distribution shape realized by the illumination part according
to the present invention;

[0019]FIG. 5 is a diagram showing a fourth example of an illumination
intensity distribution shape realized by the illumination part according
to the present invention;

[0020]FIG. 6 is a diagram showing a fifth example of an illumination
intensity distribution shape realized by the illumination part according
to the present invention;

[0021]FIG. 7 is a diagram showing a first example of an optical element
included in an illumination intensity distribution control part according
to the present invention;

[0022]FIG. 8 is a diagram showing an example of an embodiment of
measurement means and adjustment means for state of illumination light in
an illumination part according to the present invention;

[0023]FIG. 9 is a diagram showing an example of means for reducing energy
per single pulse by division and combination of optical paths in the
illumination part according to the present invention;

[0024] FIG. 10 is a diagram showing energy reduction result per single
pulse by the division and the combination of optical paths;

[0025] FIG. 11 is a diagram showing an illumination distribution shape and
a scanning direction on the surface of a sample according to the present
invention;

[0026]FIG. 12 is a diagram showing a locus of an illumination spot by
scanning;

[0027]FIG. 13 is a diagram as viewed from the side and showing
arrangement and detection directions of detection parts according to the
present invention;

[0028]FIG. 14 is a diagram as viewed from the upper side and showing
arrangement and detection directions of low-angle detection parts
according to the present invention;

[0029]FIG. 15 is a diagram as viewed from the upper side and showing
arrangement and detection directions of high-angle detection parts
according to the present invention;

[0030]FIG. 16 is a diagram showing a first example of the structure of a
detection part according to the present invention;

[0031]FIG. 17 is a diagram showing a second example of the structure of a
detection part according to the present invention;

[0032]FIG. 18 is a diagram showing a first example of plural-pixel sensor
of a detection part according to the present invention;

[0033]FIG. 19 is a diagram showing a first example of an array sensor in
a detection part according to the present invention;

[0034] FIG. 20 is a diagram showing an equivalent circuit of constituent
elements of the array sensor;

[0035] FIG. 21 is a diagram showing an embodiment of a signal processing
part according to the present invention;

[0036] FIG. 22 is a diagram showing a second example of an array sensor
according to the present invention; and

[0037] FIG. 23 is a diagram showing a second example of plural-pixel
sensor of a detection part according to the present invention.

DESCRIPTION OF EMBODIMENTS

[0038]FIG. 1 shows an example schematically illustrating the embodiment.
There are provided an illumination part 101, a detection part 102, a
stage 103 on which a sample W can be put, a signal processing part 105, a
control part 53, a display part 54 and an input part 55. The illumination
part 101 includes a laser light source 2, an attenuator 3, an emitted
light adjustment part 4, a beam expander 5, a polarization control part 6
and an illumination intensity distribution control part 7. A laser light
beam emitted from the laser light source 2 is adjusted to a desired beam
intensity by the attenuator 3 to enter the emitted light adjustment part
4 in which the adjusted light beam is further adjusted to have desired
beam position and beam traveling direction. The light beam adjusted by
the adjustment part 4 is adjusted to have a desired beam diameter by the
beam expander 5 and further adjusted to have a desired polarization state
by the polarization control part 6. The light beam adjusted by the
polarization control part 6 is adjusted to have desired intensity
distribution by the illumination intensity distribution control part 7
and to illuminate an inspection target area of the sample W.

[0039] An incident angle of the illumination light on the surface of the
sample is decided by a position and an angle of reflecting mirrors of the
emitted light adjustment part 4 disposed in an optical path of the
illumination part 101. The incident angle of the illumination light is
set to an angle suitable for detection of a minute defect. As the
incident angle of the illumination light is larger, that is, as the
elevation angle of the illumination light (angle between the sample
surface and an optical axis of the illumination light) is smaller,
scattered light (named haze) from minute unevenness on the surface of the
sample which is noise to scattered light from minute foreign matter on
the sample surface is weak and accordingly it is suitable for detection
of the minute defect. For this reason, when the scattered light from the
minute unevenness on the sample surface disturbs detection of the minute
defect, the incident angle of the illumination light may be preferably
set to be equal to or larger than 75 degrees (equal to or smaller than 15
degrees for the elevation angle). On the other hand, as the incident
angle of the illumination light is smaller in the obliquely incident
illumination, an absolute amount of scattered light from minute foreign
matter is larger and accordingly when insufficiency of an amount of
scattered light from the defect disturbs detection of the minute defect,
the incident angle of the illumination light may be preferably set to be
equal to or larger than 60 degrees and equal to or smaller than 75
degrees (equal to or larger than 15 degrees and equal to or smaller than
30 degrees for the elevation angle). Further, when the obliquely incident
illumination is performed, the polarization of the illumination light is
set to P polarization by polarization control in the polarization control
part 6 of the illumination part 101, so that the scattered light from the
defect on the sample surface is increased as compared with other
polarization. Moreover, when the scattered light from minute unevenness
on the sample surface disturbs detection of the minute defect, the
polarization of the illumination light is set to S polarization, so that
the scattered light from the minute unevenness on the sample surface is
reduced as compared with other polarization.

[0040] Further, if necessary, as shown in FIG. 1, a mirror 21 is inserted
in the optical path of the illumination part 101 and other mirrors are
disposed properly to thereby change the optical path of the illumination
light, so that the sample surface is irradiated with the illumination
light in the substantially perpendicular direction to the sample surface
(perpendicular illumination). At this time, the illumination intensity
distribution on the sample surface is controlled by an illumination
intensity distribution control part 7v similarly to the obliquely
incident illumination. In order to obtain scattered light from a hollow
defect (scratch in grinding or crystal defect in crystal material) on the
sample surface and the obliquely incident illumination by inserting a
beam splitter in the same position as the mirror 21, the vertical
illumination in which the illumination light enters the sample surface
substantially perpendicularly thereto is suitable. Further, an
illumination intensity distribution monitor 24 shown in FIG. 1 is
described later in detail.

[0041] As the laser light source 2, a laser light source which generates
an ultraviolet or vacuum ultraviolet laser beam having a short wavelength
(equal to or smaller than 355 nm) as the wavelength difficult to
penetrate into the sample and has high output equal to or larger than 2 W
is used in order to detect the minute defect near the sample surface. A
diameter of the emitted light beam is about 1 mm. In order to detect a
defect in the sample, a laser light source which generates visible or
infrared laser beam as a wavelength easy to penetrate into the sample is
used.

[0042] The attenuator 3 includes a first polarizing plate, a half-wave
plate which is rotatable about the optical axis of the illumination light
and a second polarizing plate. Light which enters the attenuator 3 is
converted into linearly polarized light by the first polarizing plate and
the polarization direction thereof is rotated in any direction in
accordance with an azimuth angle of a slow axis of the half-wave plate.
The light having the polarization direction rotated passes through the
second polarizing plate. The azimuth angle of the half-wave plate is
controlled to thereby reduce the light intensity at any ratio. When the
linear polarization degree of the light entering the attenuator 3 is
sufficiently high, the first polarizing plate is not necessarily
required. The attenuator 3 in which the relation between the input signal
and the light reduction ratio is previously calibrated is used. As the
attenuator 3, an ND filter having gradation concentration distribution
can be also used or ND filters having plural concentrations different
from one another can be also switched to be used.

[0043] The emitted light adjustment part 4 includes plural reflecting
mirrors. In the embodiment, the emitted light adjustment part 4 composed
of two reflecting mirrors is described, although the emitted light
adjustment part 4 is not limited thereto and the emitted light adjustment
part 4 may use three or more reflecting mirrors. Here, it is assumed that
the three-dimensional orthogonal coordinate system (XYZ coordinates) is
defined and incident light on the reflecting mirror travels in +X
direction. The first reflecting mirror is installed to deflect the
incident light in +Y direction (incidence and reflection in XY planes)
and the second reflecting mirror is installed to deflect light reflected
by the first reflecting mirror in +Z direction (incidence and reflection
in YZ planes). A position and a traveling direction (angle) of light
emitted from the emitted light adjustment part 4 are adjusted by means of
parallel movement and adjustment of the elevation angle of the respective
mirrors. As described above, the first and second reflecting mirrors are
disposed so that incidence and reflection planes (XY planes) of the first
reflecting mirror and incidence and reflection planes (YZ planes) of the
second reflecting mirror are orthogonal with each other to thereby make
it possible to adjust the position and the angle in XZ planes and the
position and the angle in YZ planes of light (traveling in +Z direction)
emitted from the emitted light adjustment part 4.

[0044] The beam expander 5 includes two or more lens groups and has the
function of enlarging a diameter of incident parallel light flux. For
example, a beam expander of Galileo type having a concave lens and a
convex lens in combination is used. The beam expander 5 is installed on a
translation stage having two or more axes and can adjust the position
thereof so that the center thereof is identical with a predetermined beam
position. Further, the beam expander 5 has the elevation angle adjustment
function of the whole beam expander 5 so that the optical axis of the
beam expander 5 is identical with a predetermined beam optical axis. A
space between lenses can be adjusted to control an enlargement ratio of a
diameter of the light flux (zoom mechanism). When light incident on the
beam expander 5 is not parallel, enlargement of the diameter and
collimation (quasi-collimation of light flux) of the light flux are
performed at the same time by adjustment of the space between lenses. The
collimation of the light flux may be made by installing a collimating
lens independent of the beam expander 5 at the upper stream of the beam
expander 5. The enlargement ratio of the beam diameter by the beam
expander 5 is about 5 to 10 times and the light beam emitted from the
light source and having a diameter of 1 mm is enlarged from 5 mm to 10
mm.

[0045] The polarization control part 6 is composed of a half-wave plate
and a quarter-wave plate and controls the polarization state of the
illumination light to any polarization state. State of light incident on
the beam expander 5 and the illumination intensity distribution control
part 7 is measured by a beam monitor 22 on the way of the optical path of
the illumination part 101.

[0046] FIGS. 2 to 6 schematically illustrate the positional relation
between an illumination optical axis 120 led to the sample surface by the
illumination part 101 and the illumination intensity distribution shape.
The structure of the illumination part 101 in FIGS. 2 to 6 shows part of
the structure of the illumination part 101, and the emitted light
adjustment part 4, the mirror 21, the beam monitor 22 and the like are
omitted. FIG. 2 schematically illustrates a section of an incident plane
of obliquely incident illumination (containing illumination optical axis
and a normal line to the sample surface). The obliquely incident
illumination is oblique to the sample surface in the incident plane. The
substantially uniform illumination intensity distribution is formed in
the incident plane by the illumination part 101. The length of part where
the illumination intensity is uniform is about 100 μm to 4 mm since
wide area per unit time is inspected. FIG. 3 schematically illustrates a
section of a plane containing the normal line to the sample surface and
perpendicular to the incident plane of the obliquely incident
illumination. The illumination intensity distribution on the sample
surface in the plane has the peripheral part in which the intensity is
weak as compared with the center. More particularly, the illumination
intensity distribution is the Gaussian distribution in which the
intensity distribution of light incident on the illumination intensity
distribution control part 7 is reflected or the intensity distribution
similar to first-class first-degree Bessel function in which an opening
shape of the illumination intensity distribution control part 7 is
reflected or sinc function. The length of the illumination intensity
distribution (length of area having the illumination intensity equal to
or larger than 13.5% of the maximum illumination intensity) in the plane
is shorter than the length of part where the illumination intensity in
the incident plane is uniform and is about 2.5 to 20 μm since haze
generated from the sample surface is reduced. The illumination intensity
distribution control part 7 includes optical elements such as aspheric
lens, diffractive optical element, cylindrical lens array and light pipe
described later. The optical elements constituting the illumination
intensity distribution control part 7 are installed perpendicularly to
the illumination optical axis as shown in FIGS. 2 and 3.

[0047] The illumination intensity distribution control part 7 includes an
optical element acting on the phase distribution and the intensity
distribution of incident light. A diffractive optical element (DOE) 71 is
used (FIG. 7) as the optical element constituting the illumination
intensity distribution control part 7. The diffractive optical element 71
includes minute undulating shape having a size equal to or smaller than
the wavelength of light and formed on the surface of a substrate made of
material which transmits the incident light. Molten quartz is used for
ultraviolet rays as the material which transmits the incident light. In
order to suppress attenuation of light caused by passage of the
diffractive optical element 71, it is better to use the diffractive
optical element subjected to coating using a reflection prevention film.
The lithography method is used to form the minute undulating shape. When
light which becomes quasi-collimated light after passage of the beam
expander 5 passes through the diffractive optical element 71, the
illumination intensity distribution is formed on the sample surface in
accordance with the undulating shape of the diffractive optical element
71. The undulating shape of the diffractive optical element 71 is
designed and manufactured to have a shape requested on the basis of
calculation using the Fourier optical theory so that the illumination
intensity distribution formed on the sample surface is long and uniform
distribution in the incident plane. The optical element included in the
illumination intensity distribution control part 7 is provided with a
translation adjustment mechanism having two or more axes and a rotation
adjustment mechanism having two or more axes so that relative position
and angle of the incident light to the optical axis can be adjusted.
Furthermore, a focus adjustment mechanism using movement in the optical
axis direction is provided. As a substitute optical element having the
same function as the diffractive optical element 71, an aspheric lens, a
combination of cylindrical lens array and cylindrical lens and a
combination of light pipe and focusing lens may be used.

[0048] The state of illumination light in the illumination part 101 is
measured by the beam monitor 22. The beam monitor 22 measures position
and angle (in the traveling direction) of the illumination light passing
through the emitted light adjustment part 4 or position and wave surface
of the illumination light incident on the illumination intensity
distribution control part 7 to be outputted. The measurement of position
of the illumination light is made by measuring the position in the center
of gravity of light intensity of the illumination light. As a concrete
position measurement means, a position sensitive detector (PSD) or an
image sensor such as CCD sensor and CMOS sensor is used. The measurement
of angle of the illumination light is made by an optical position sensor
or an image sensor installed in a position far distant from the light
source than the position measurement means or in a focused position of
the collimating lens. The position and the angle of illumination light
measured by the beam monitor 22 are supplied to the control part 53 to be
displayed in the display part 54. When the position or the angle of
illumination light is shifted from a predetermined position or angle, the
emitted light adjustment part 4 adjusts the position or the angle of
illumination light to be returned to predetermined position.

[0049] The measurement of wave surface of the illumination light is made
in order to measure a parallel degree of light incident on the
illumination intensity control part 7. Measurement using a sharing
interferometer or a Shack Hartman wave surface sensor is performed. The
sharing interferometer includes optical glass having both sides polished
evenly and a thickness of about several mm and which is inserted in the
optical path of the illumination light obliquely and measures emanation
and convergence states of the illumination light by pattern of
interference fringes observed when reflected light from the surface and
reflected light from the back are projected on a screen. As the sharing
interferometer, there is SPUV-25 made by a SIGMA KOKI Co., Ltd. or the
like. When an image sensor such as CCD sensor and CMOS sensor is disposed
in a screen position, the emanation and convergence states of the
illumination light can be measured automatically. The Shack Hartman wave
surface sensor includes a small lens array which divides wave surface to
project divided wave surfaces on an image sensor such as CCD sensor and
measures inclination of individual wave surfaces from displacement of the
projection position. Detailed measurement of wave surface such as
disturbance of partial wave surface can be made as compared with the
sharing interferometer. When it becomes clear from the measurement of
wave surface that light incident on the illumination intensity control
part 7 is not quasi-collimated light and is emanated or converged, a lens
group of the beam expander 5 at a pre-stage can be displaced in the
optical axis direction to approach the quasi-collimated light. Further,
when it becomes clear from the measurement of wave surface that the wave
surface of light incident on the illumination intensity control part 7 is
partially inclined, a spatial light phase modulation element which is a
kind of a spatial light modulator (SLM) can be inserted in the pre-stage
of the illumination intensity control part 7 to give proper phase
difference to each position of the section of light flux so that the wave
surface is even to thereby make the wave surface approach to be even,
that is, make the illumination light approach the quasi-collimated light.
The accuracy of wave surface (shift from the predetermined wave surface
(design value or initial state) of light incident on the illumination
intensity distribution control part 7 can be suppressed to λ/10 rms
or less by means of the wave surface accuracy measurement and adjustment
means described above.

[0050] The illumination intensity distribution on the sample surface
adjusted by the illumination intensity distribution control part 7 is
measured by the illumination intensity distribution monitor 24. Further,
as shown in FIG. 1, even when the vertical illumination is used, the
illumination intensity distribution on the sample surface adjusted in the
illumination intensity distribution control part 7v is measured by the
illumination intensity distribution monitor 24 similarly. The
illumination intensity distribution monitor 24 focuses the sample surface
on an image sensor such as CCD sensor and CMOS sensor through a lens to
be detected as an image. The image of the illumination intensity
distribution detected by the illumination intensity distribution monitor
24 is processed in the control part 53 so that a position of the center
of gravity of intensity, a maximum intensity, a position of the maximum
intensity, width and length of the illumination intensity distribution
(width and length of the illumination intensity distribution area
exceeding predetermined intensity or predetermined ratio to the maximum
intensity value) and the like are calculated to be displayed in the
display part 54 together with an outline shape and a sectional shape of
the illumination intensity distribution.

[0051] When the obliquely incident illumination is made, positional
displacement of the illumination intensity distribution due to
displacement in height of the sample surface and disturbance of the
illumination intensity distribution due to defocusing occur. In order to
suppress it, the height of the sample surface is measured and when the
height is shifted, the shift is corrected by the illumination intensity
distribution control part 7 or adjustment of the height in the Z axis of
the stage 103. FIG. 8 schematically illustrates an example of the
illumination part and the part concerning measurement and correction of
the illumination light of the embodiment. The height of the sample
surface is measured by means of a light beam emission part 31 and a light
receiving part 32 which receives light emitted from the light beam
emission part 31 and reflected on the sample surface. The light beam
emission part 31 includes a light source such as a semiconductor laser
and a floodlighting lens. The light receiving part 32 includes a light
receiving lens and an optical position sensor. Since the sample surface
having strong gloss such as the surface of a semiconductor silicon and
the surface of a magnetic disk substrate or board is measured, the light
beam emission part 31 and the light receiving part 32 are disposed so
that light emitted from the light beam emission part 31 and regularly
reflected on the sample surface can be received by the light receiving
part 32. The displacement of height of the sample surface is detected as
positional shift of a light spot detected by the optical position sensor
of the light receiving part 32 using the theory of triangular surveying.

[0052] The positional shift in the in-plane direction of the sample
surface of the illumination light irradiation position due to the
displacement in height of the sample surface is corrected by adjustment
of deflection angle by deflection means 33 which is disposed downstream
of the illumination intensity distribution control part 7 and directs the
illumination light to the sample surface. The deflection means 33
includes a reflecting mirror which deflects the illumination light and a
piezo element which controls the elevation angle to the optical axis of
the illumination light of the reflecting mirror. The deflection means 33
controls the elevation angle within a range of about ±1 mrad by using
a frequency of 400 Hz or more. The positional shift in the in-plane
direction of the sample surface of the illumination light irradiation
position is calculated from the measurement value of displacement in
height and the incident angle of the illumination light and a control
signal outputted from the control part 53 is received by the deflection
means 33 to control the reflecting mirror so that the shift is corrected.
The positional shift in the in-plane direction of the sample surface of
the illumination light irradiation position can be also corrected by
directly measuring the position of the center of gravity of the
illumination intensity distribution using the illumination intensity
distribution monitor 24. When the positional shift in the in-plane
direction of the sample surface of the illumination light irradiation
position due to displacement in height of the sample surface is corrected
by the deflection means 33, the length of optical path between the
illumination intensity distribution control part 7 and the sample surface
is deviated or differentiated as compared with the state that the
correction is not made and accordingly defocusing of an illumination spot
occurs depending on the shift amount. The shift amount of the length of
optical path is calculated from the measurement value of displacement in
height and the incident angle of the illumination light and the
defocusing is reduced by positional adjustment in the optical axis
direction of the optical element provided in the illumination intensity
distribution control part 7 or adjustment of emanation angle of the beam
expander 5 on the basis of the calculated shift amount.

[0053] When a pulse laser which is easy to produce high output is used as
the light source 2, illumination energy given to the sample is
concentrated in a moment that pulse is inputted and accordingly the
sample is sometimes subjected to thermal damage caused by instantaneously
increased temperature due to inputting of the pulse. In order to avoid
it, the optical path of the pulse laser is branched or divided and a
difference is given between the branched optical paths. Then, the
branched optical paths are combined, so that energy per one pulse can be
reduced effectively while the total energy is maintained as shown in FIG.
10.

[0054]FIG. 9 shows an example of an optical system for implementing the
above operation. The illumination light passing through the beam expander
5 is branched or divided by a polarizing beam splitter 151 into light
passing through a first optical path formed by reflecting the light by
the polarizing beam splitter 151 and light passing through a second
optical path formed by light passing through the polarizing beam splitter
151. Light passing through the first optical path is reflected by a
retroreflector 152 to be returned and is then reflected by a polarizing
beam splitter 153 to be combined with light passing through the second
optical path. The retroreflector 152 includes two or more reflecting
mirrors orthogonal with each other and returns input light in the
opposite direction of 180 degrees. The retroreflector is also named a
corner cube. Two or more independent reflecting mirrors may be used
instead of the retroreflector. In order to make the intensity of the
light reflected by the polarizing beam splitter 151 equal to the
intensity of the light passing through the polarizing beam splitter, a
wave plate 150 is used to adjust polarization of the illumination light
to be circular polarization or linear polarization of 45 degrees in
inclination. When the difference between the first and second optical
paths is L, the time interval between a pulse of light passing through
the first optical path and a pulse of light passing through the second
optical path is Δtp=L/c. The time interval Δtp is made equal
to or larger than the time required to suppress increase of temperature
at the time that a single pulse is inputted, so that instantaneous
increase of temperature of the sample by the single pulse and increase of
temperature due to thermal accumulation by plural pulses can be
suppressed.

[0055] Referring to FIGS. 11 and 12, an illumination distribution shape
(illumination spot 20) formed on the sample surface by the illumination
part 101 and a sample scanning method are described. A circular
semiconductor silicon wafer is supposed as the sample W. The stage 103
includes a translation stage, a rotation stage and a Z stage for
adjustment of height of the sample surface (all not shown). The
illumination spot 20 has the illumination intensity distribution which is
long in one direction as described above and the direction thereof is S2.
The direction that is substantially orthogonal to the direction S2 is
supposed to S1. Scanning is made in the circumferential direction S1 of a
circle having a rotation axis of the rotation stage as the center thereof
by rotation motion of the rotation stage and in the translational
direction S2 of the translation stage by translation motion of the
translation stage. The scanning is made by the length equal to or shorter
than the length in the longitudinal direction of the illumination spot 20
in the scanning direction S2 while the sample makes one rotation by
scanning in the scanning direction S1, so that a spiral locus T is drawn
on the sample W by the illumination spot to thereby scan the whole
surface of the sample 1.

[0056] The plural detection parts 102 are disposed to detect scattered
light in plural directions emitted from the illumination spot 20. An
example of arrangement of the sample W and the illumination spot 20 in
the detection part 102 is described with reference to FIGS. 13 to 15.
FIG. 13 is a side view showing arrangement of the detection parts 102. An
angle of a detection direction (the central direction of detection
opening) by the detection part 102 to the normal line of the sample W is
defined as a detection zenith angle. The detection parts 102 include
high-angle detection parts 102h having the detection zenith angle of 45
degrees or less and low-angle detection parts 102l having the detection
zenith angle of 45 degrees or more. The high-angle detection parts 102h
and the low-angle detection parts 102l each include plural detection
parts so that light scattered in numerous directions in each detection
zenith angle is covered. FIG. 14 is a plan view showing arrangement of
the low-angle detection parts 102l. An angle between the traveling
direction of the obliquely incident illumination and the detection
direction in the plane parallel to the surface of the sample W is defined
as a detection azimuth angle. The low-angle detection parts 102 include a
low-angle front detection part 102lf, a low-angle side detection part
102ls and a low-angle back detection part 102lb and further the low-angle
detection parts 102 include a low-angle front detection part 102lf', a
low-angle side detection part 102ls' and a low-angle back detection part
102lb' arranged in symmetrical positions with respect to the above
detection parts 102lf, 102ls and 102lb in the illumination incident
plane, respectively. For example, the low-angle front detection part
102lf is installed to have the detection azimuth angle equal to or larger
than 0 degree and equal to or smaller than 60 degrees, the low-angle side
detection part 102ls is installed to have the detection azimuth angle
equal to or larger than 60 degrees and equal to or smaller than 120
degrees, and the low-angle back detection part 102lb is installed to have
the detection azimuth angle equal to or larger than 120 degrees and equal
to or smaller than 180 degrees. FIG. 15 is a plan view showing
arrangement of the high-angle detection parts 102h. The high-angle
detection parts 102 include a high-angle front detection part 102hf, a
high-angle side detection part 102hs, a high-angle back detection part
102hb and a high-angle side detection part 102hs' arranged in a
symmetrical position with respect to the high-angle side detection part
102hs in the illumination incident plane. For example, the high-angle
front detection part 102hf is installed to have the detection azimuth
angle equal to or larger than 0 degree and equal to or smaller than 45
degrees, the high-angle side detection part 102hs is installed to have
the detection azimuth angle equal to or larger than 45 degrees and equal
to or smaller than 135 degrees and the high-angle back detection part
102hb is installed to have the detection azimuth angle equal to or larger
than 135 degrees and equal to or smaller than 180 degrees. Here, four
high-angle detection parts 102h and six low-angle detection part 102l are
provided, although the present invention is not limited thereto and the
number and the position of the detection parts may be changed properly.

[0057]FIG. 16 shows an example illustrating the concrete structure of the
detection part 102. The scattered light emitted from the illumination
spot 20 is focused by an objective lens 201 and after the focused light
passes through a polarizing filter 202, the light is led to light
receiving plane of plural-pixel sensor 204 by a focusing lens 203 to be
detected. In order to detect the scattered light efficiently, it is
preferable that detection NA of the objective lens is equal to or larger
than 0.3. In case of the low-angle detection part, a lower end of the
objective lens 201 is cut off if necessary so that the lower end of the
objective lens 201 does not interfere with the sample surface W. The
polarizing filter 202 is constituted of a polarizing plate or polarizing
beam splitter and is installed to cut linear polarization component in
any direction. A wire grid polarizing plate or polarizing beam splitter
having the transmission factor equal to or larger than 80% is used as the
polarizing plate. When any polarization component containing elliptical
polarization is cut, the polarizing filter 202 including a wave plate and
a polarizing plate is installed.

[0058]FIG. 18 schematically illustrates the structure of the plural-pixel
sensor 204. An image of the sample surface is focused on a plane 205
conjugate to the sample surface by the objective lens 201 and the
focusing lens 203. A defect image 221 and one-axis enlarged image 225 of
the defect image in FIG. 18 schematically illustrate an example of the
state in which the defect is positioned in the center of the visual field
for detection of the detection part 102. After the defect image 221 is
once focused on conjugate plane 225 to the sample surface, the defect
image travels in the optical axis direction of the detection part 102
with spread angle conforming to NA on the image side of the focusing lens
203. This light beam is focused in the direction corresponding to the
scanning direction S2 on the conjugate plane 205 to the sample surface by
means of one-axis focusing system 223 to be focused on the light
receiving plane of an array sensor 224. The light beam in the direction
corresponding to the scanning direction S1 on the conjugate plane 205 to
the sample surface reaches the light receiving plane of the array sensor
224 with the spread angle.

[0059] The one-axis focusing system 223 has the function that light is
focused only in the direction corresponding to the scanning direction S1
and is composed of a cylindrical lens or a combination of cylindrical
lens and spherical lens. The defect image 221 is spread or enlarged in
the direction corresponding to the scanning direction S1 by the one-axis
focusing system 223. A size of the defect image on the conjugate plane
205 to the sample surface is decided by the optical resolution degree of
the detection part 102 in case of minute defect smaller than the
wavelength of the illumination light and is concretely decided by NA on
the image side of the focusing lens 203 (the size of image of the minute
defect (spread point image)=1.22×(wavelength)/(NA on image side)).
The length in the S1 direction of the one-axis enlarged image 225 of the
defect image, that is, the enlargement ratio in the S1 direction is
decided by the length of the optical path between the conjugate plane 205
to the sample surface and the light receiving plane of the array sensor
224 and NA on the image side of the focusing lens 203. The plural-pixel
sensor 204 is constructed so that the length in the S1 direction of the
one-axis enlarged image 225 of the defect image is substantially equal to
the length in the S1 direction of the light receiving plane of the array
sensor 224. The width in the S2 direction of the one-axis enlarged image
225 of the defect image is decided by magnification of the one-axis
focusing system 223. The plural-pixel sensor 204 is constructed so that
the length is equal to or shorter than the length in the S2 direction of
the light receiving plane of the array sensor 224.

[0060] The scattered light from the sample surface is generated from
position of the illumination spot 20 and detected by the detection part
102, although even an area on the outside of the illumination spot 20 is
substantially irradiated with the illumination light having relatively
weak intensity because of the wave motion nature of light. Consequently,
there is a case where part of scattered light generated by large foreign
matter on the outside of the illumination spot 20 or edge at an end of
the sample surface enters the light receiving plane of the array sensor
224 and becomes noise to reduce the sensitivity. When this causes a
problem, a shielding slit 222 can be disposed so that obstructive
scattered light can be shielded to be reduced. The shielding slit has a
slit opening (light transmission part) having the width wider than the
width of image on the illumination spot 20 on the conjugate plane 205 to
the sample surface and the shielding slit is disposed so that the center
of the slit opening is identical with the position of the image on the
illumination spot 20. Since the other area except the opening is
shielded, the scattered light from the other area except the area on the
sample surface on which the illumination spot 20 is impinged is reduced.

[0061]FIG. 19 shows an example schematically illustrating the light
receiving plane of the array sensor 224. The array sensor 224 includes
plural avalanche diodes (APD) arranged two-dimensionally. Hereinafter,
each APD of the receiving part is named an APD pixel. APD pixels 231 each
are applied with a voltage so that each of them is operated in the Geiger
mode (photoelectron multiplication factor is equal to or larger than
105). When one photon enters the APD pixel 231, photoelectrons are
generated in the APD pixel 231 with the probability according to the
quantum efficiency of the APD pixel and are multiplied by action of the
APD in the Geiger mode, so that an electrical pulse signal is produced.
An APD pixel row 232 in S1 direction (a collection of APD pixels enclosed
by a quadrilateral 232 of broken line in FIG. 19) is defined as one unit
and the electrical pulse signals generated in the APD pixels contained in
the pixel row are totalized in each APD pixel row in the S1 direction to
be outputted. Plural APD pixel rows are arranged in S2 direction and
output signals of the APD pixels in the plural rows are outputted in
parallel.

[0062] FIG. 20 shows an example of a circuit diagram equivalent to one APD
pixel row 232 in the S1 direction. In FIG. 20, a pair of one quenching
resistor 226 and APD 227 corresponds to one APD pixel 231. Each APD is
applied with an reverse voltage VR. The reverse voltage is set to be
equal to or higher than a breakdown voltage of the APD so that the APD
227 is operated in the Geiger mode. With the circuit configuration shown
in FIG. 20, an electrical output signal (peak value of voltage or current
or electric charge amount) proportional to the total number of photons
incident on the APD pixel row 232 in S1 direction is obtained. The
electrical output signals (peak value of voltage or current or electric
charge amount) corresponding to the APD pixel rows 232 in S1 direction
are converted from analog signals to digital signals and outputted in
parallel as the digital signal in time series.

[0063] The individual APD pixels output only the pulse signal to the same
degree as in the case where one photon is incident even if plural photons
are incident in a short time and accordingly when the number of incident
photons per unit time on the individual APD pixels is increased, the
total output signal of the APD pixel row is not proportional to the
number of incident photons and the linearity of signal is deteriorated.
Further, when incident light exceeding a fixed amount (about one photon
on average per pixel) enters all pixels in the APD pixel row, an output
signal is saturated. Arrangement of the large number of APD pixels in the
S1 direction can reduce the incident light amount per pixel and counting
of photons can be made more correctly. For example, when the number of
pixels in the S1 direction is 1000, sufficient linearity can be ensured
with optical intensity equal to or smaller than about 1000 photons per
unit time of detection in case where the quantum efficiency of APD pixels
is 30% and the optical intensity equal to or smaller than about 3300
photons can be detected without saturation.

[0064] In the structure of the plural-pixel sensor 204 shown in FIG. 18,
the optical intensity in the S1 direction is not uniform and the optical
intensity at ends of the array sensor 224 is weak as compared with the
center of the array sensor 224. This means that the number of effective
APD pixels in the S1 direction is reduced. A lenticular lens composed of
a lot of minute cylindrical lenses having the curvature in the S1
direction and arranged in the S1 direction instead of cylindrical lenses,
diffraction-type optical elements or spherical lenses can be used to make
the distribution in the S1 direction of the one-axis enlarged image 225
of the defect image have uniform intensity. By doing so, the optical
intensity range in which the linearity can be ensured or the optical
intensity range in which saturation does not occur can be extended while
the number of APD pixels in the S1 direction is maintained.

[0065] With the structure of the plural-pixel sensor 204 described above,
the number of photons at each position in the S2 direction on the
conjugate plane 205 to the sample surface can be counted in parallel at
the same time.

[0066]FIG. 17 shows a modification example illustrating the concrete
structure of the detection part 102. The scattered light emitted from the
illumination spot 20 is focused by the objective lens 201 and after the
focused light passes through the polarizing filter 202, the light is
focused on a diffraction grating 206 disposed on a plane conjugate to the
sample surface to form an image (intermediate image) of the sample
surface. The image of the sample surface formed on the diffraction
grating 206 is projected on the light receiving plane of the plural-pixel
sensor 204 by an image forming system 207 to be detected. The
plural-pixel sensor 204 is disposed in the plane conjugate to the sample
surface so that the arrangement direction of pixels is identical with the
longitudinal direction of the image of the illumination spot 20 in
accordance with the shape of the illumination spot 20 which is extended
in one direction. As the diffraction grating 206, the diffraction grating
having a formed diffraction grating shape is used so that Nth degree
diffracted light of incident light along the optical axis of the light
led by the focusing lens 203 to form the intermediate image is directed
in the normal direction of the surface of the diffraction grating 206 in
order to diffract the light led by the focusing lens 203 to form the
intermediate image into the normal direction of the surface of the
diffraction grating 206. In order to enhance the diffraction efficiency,
a blaze diffraction grating is used. By disposing the plural-pixel sensor
204 on the plane conjugate to the sample surface with the above
structure, deviation of focusing can be reduced even in the S1 direction
on the sample surface to ensure effective visual field in the wide range
and the scattered light can be detected with reduced loss in light
amount.

[0067] The relation of the length of the illumination spot 20, the optical
magnification of the detection part 102 and the dimension of the
plural-pixel sensor 204 is described. When the high-sensitivity and
high-speed inspection is performed, the length of the illumination spot
20 is set to about 500 μm. When the plural-pixel sensor 204 having 100
pixels arranged at intervals of 25 μm in the S2 direction (100 APD
pixel rows 232 are arranged in the S1 direction) is installed, the
optical magnification of the detection part is 5 times and the interval
of pixels projected on the sample surface is 5 μm.

[0068] When the sample is rotated at the rotation speed of 2000 rpm on the
above condition, all surface of a circular sample having a diameter of
300 mm is scanned in 9 seconds and all surface of a circular sample
having a diameter of 450 mm is scanned in 14 seconds. Further, when
inspection is performed at higher speed, the length of the illumination
spot 20 is set to about 100 μm. In this case, the optical
magnification of the detection part is 0.4 times and the interval of
pixels projected on the sample surface is 62.5 μm. When the sample is
rotated at the rotation speed of 2000 rpm on this condition, all surface
of a circular sample having a diameter of 300 mm is scanned in 5 seconds
and all surface of a circular sample having a diameter of 450 mm is
scanned in 7 seconds.

[0069] Next, referring to FIG. 21, a signal processing part 105 which
classifies various kinds of defects and presumes dimensions of the
defects with high accuracy on the basis of intensity detection signals of
scattered light in various directions detected at the same time by plural
detection optical systems which cover a wide angular range is described.
Here, for the sake of simplicity, the structure of the signal processing
part 105 having two systems of detection parts 102a and 102b (not shown)
of plural detection parts 102 is described. Further, each of the
detection parts 102a and 102b produces signal for each APD pixel row.
Here, description is made while attention is paid to the signal of one
pixel row thereof, although it is needless to say that the same
processing is performed even for other pixel rows in parallel. Output
signals 500a and 500b outputted from the detectors included in the
detection parts 102a and 102b and corresponding to detected scattered
light amounts are supplied to a digital processing part 52 in which
defect signals 603a and 603b are extracted by high-pass filters 604a and
604b to be supplied to a defect judgment part 605. Since defects are
scanned in the S1 direction by the illumination spot 20, the waveform of
the defect signals is enlargement or reduction of an illumination
distribution profile in the S1 direction of the illumination spot 20.
Accordingly, the high-pass filters 604a and 604b are used to make the
defect signal pass through a frequency band containing defect signal
waveform to thereby cut the frequency band and the DC component
containing much noise relatively, so that S/N of the defect signals 603a,
603b is improved. As the high-pass filters 604a, 604b, high-pass filters
or band-pass filters designed to have a specific cut-off frequency and
cut off the frequency component exceeding the frequency or FIR filters
having a similar figure to the waveform of the defect signals on which
the shape of the illumination spot 20 is reflected may be used. The
defect judgment part 605 subjects input of signals containing the defect
waveform outputted from the high-pass filters 604a, 604b to threshold
processing to judge whether defect is present or not. That is, the defect
judgment part 605 is supplied with the defect signals based on the
detection signals from the plural detection optical systems and
accordingly the defect judgment part 605 subjects the sum or the weighted
average of plural defect signals to threshold processing or takes OR or
AND of defect groups extracted by the threshold processing to which the
plural defect signals are subjected on the same coordinate system set on
the surface of wafer, so that the defects can be inspected with high
sensitivity as compared with defect inspection based on a single defect
signal.

[0070] Further, the defect judgment part 605 supplies defect coordinates
indicating a defect position in the wafer and presumed values of
dimensions of the defect calculated on the basis of the defect waveform
and a sensitivity information signal in a place judged that the defect is
present to the control part 53 as defect information to be outputted to
the display part 54 or the like. The defect coordinates are calculated
using the center of gravity of the defect waveform as a reference. The
defect dimensions are calculated on the basis of an integrated value or a
maximum value of the defect waveform.

[0071] Moreover, output signals from analog processing part 51 are
supplied to each of low-path filters 601a and 601b in addition to the
high-path filters 604a and 604b constituting the digital processing part
52 and the low-path filters 601a and 601b produce direct current
components and low frequency components corresponding to scattered light
amount (haze) from minute roughness in the illumination spot 20 on the
wafer. In this manner, outputs from the low-path filters 601a and 601b
are supplied to a haze processing part 606 and subjected to processing of
haze information. That is, the haze processing part 605 produces a signal
corresponding to magnitude of haze in each place on the wafer from
magnitude of input signals supplied from the low-path filters 601a and
601b as haze signal. Further, since angular distribution of the scattered
light amount from the roughness is changed in accordance with spatial
frequency distribution of the minute roughness, haze signals from the
detectors of the plural detection parts 102 disposed in directions and
angles different from one another are supplied to the haze processing
part 606 as shown in FIGS. 13 to 23, so that information concerning the
spatial frequency distribution of the minute roughness can be obtained
from the haze processing part 606 on the basis of the intensity ratio
thereof.

[0072] A modification example of the illumination intensity distribution
formed on the sample surface by the illumination part 101 is described.
The illumination intensity distribution having the Gaussian distribution
in the longitudinal direction can be also used instead of the
illumination intensity distribution extended in one direction and having
the substantially uniform intensity in the longitudinal direction. The
Gaussian distribution illumination extended in one direction is formed by
the structure in which a spherical lens is included in the illumination
intensity distribution control part 7 and an elliptical beam extended in
one direction is formed by the beam expander 5 or by the structure in
which the illumination intensity distribution control part 7 is composed
of plural lenses containing cylindrical lenses. Part or all of
cylindrical lenses or spherical lens included in the illumination
intensity distribution control part 7 can be installed in parallel to the
sample surface to thereby form the illumination intensity distribution
extended in one direction on the sample surface and having the width
which is narrow in the perpendicular direction to the extended direction.
Variation of the illumination intensity distribution on the sample
surface due to variation of the state of light incident on the
illumination intensity distribution control part 7 is smaller and the
stability of the illumination intensity distribution is higher as
compared with the case where the uniform illumination intensity
distribution is formed and further the transmission factor of light is
high and the efficiency is satisfactory as compared with the case where a
diffraction optical element, a micro lens array or the like is used in
the illumination intensity distribution control part 7.

[0073] FIG. 22 schematically illustrates a modification example of the
array sensor 224. In the array sensor 224 having the arranged APD pixels,
when individual APD pixels are small, the insensible area between the APD
pixels is relatively larger than the effective area of the light
receiving part of the APD pixels and accordingly there is a problem that
the fill factor of the array sensor 224 is reduced and the light
detection efficiency is reduced. Hence, a micro lens array 228 is
disposed before the light receiving plane of the array sensor 224, so
that the ratio of light incident on the insensible area between pixels
can be reduced to thereby improve the effective fill factor. The micro
lens array 228 includes minute convex lenses arranged at the same
intervals as the arrangement intervals of the APD pixels and is disposed
so that parallel light beams (shown by broken lines in FIG. 22) to the
main optical axis of the incident light on the array sensor 224 enter the
vicinity of the center of relevant APD pixels.

[0074] FIG. 23 schematically illustrates a modification example of the
plural-pixel sensor 204. The plural-pixel sensor 204 includes one-axis
focusing system 229 having the function of focusing in the S1 direction
and one-axis focusing system 223 having the function of focusing in the
S2 direction. The focusing magnification in the S1 direction is made
higher than that in the S2 direction, so that the defect image 221 is
enlarged in the S1 direction. When cylindrical lenses are used as the
one-axis focusing systems 229 and 223, the one-axis focusing system 229
is disposed nearer to the conjugate plane 205 to the sample surface than
the one-axis focusing system 223 to form the focusing relation in the S1
direction, so that the magnification in the S1 direction is higher than
that in the S2 direction. In the structure (FIG. 18) described above, the
optical intensity distribution in the S1 direction of the one-axis
enlarged image 225 or magnitude of spread of the image is sometimes
changed depending on angular distribution in the S1 direction of the
scattered light on the conjugate plane 205 to the sample surface. In
contrast, in the embodiment, the magnitude of the one-axis enlarged image
225 is decided by magnitude of the defect image 221 and the focusing
magnification in the S1 and S2 directions decided by the structure and
arrangement of the one-axis focusing systems 229 and 223. Since the
magnitude of the defect image 221 of the minute defect is decided by the
optical resolution degree of the detection part 102 as described above,
change of the magnitude of the one-axis enlarged image 225 is small and
stable inspection result is obtained.

[0075] A photomultiplier having high electron multiplication factor
(104 or more) may be used instead of the avalanche photodiodes which
are constituent elements of the array sensor 224. Since the size of
individual pixels can be made small when the avalanche photodiodes are
used, there are merits that the optical magnification of the detection
part 102 can be reduced and integration exceeding several hundred pixels
and several thousand pixels can be made at low cost. In contrast, there
is a merit that the photomultiplier has low temperature dependence of the
electron multiplication factor and is stable.

[0076] Further, the present invention is not limited to the above
embodiments and various modification examples are contained. For example,
the above embodiments have been described in detail for easy
understanding of the present invention and are not necessarily limited to
provision of all the structure described. Moreover, part of the structure
of an embodiment may be replaced by the structure of another embodiment
and further the structure of an embodiment may be added to the structure
of another embodiment. Further, part of the structure of the embodiments
may be subjected to addition, deletion and replacement of other
structure.